Bin Li,
The APO System is something that is configured for each client based on what level of data they want to plan on. Because of this - APO gives an extractor configurator which helps you decide what fields you need to extract and then you can extract the same into BW. This setup is similar to the LO cockpit which we use in ECC.
Because of this configurability - the data models are usually specific to the client and hence you will get the extractors and would most likely build your own data models for the same.